1. Field of the Invention
The present invention relates to a heater member formed from silicon carbide, which exhibits high durability in an oxidizing atmosphere, in a vacuum atmosphere, and even in a corrosive atmosphere, and which has excellent temperature uniformity.
2. Description of the Related Art
A metallic material such as a nickel chrome alloy or a carbon material such as graphite is generally employed for a heating body of a heater member used in various types of thermal treatment equipment or in heating furnaces. In these heaters, the metallic material is corroded by oxidation or is partially melted due to heating at temperatures of 1,000.degree. C. or more and cannot withstand use at high temperatures. On the other hand, although carbon materials have excellent heat resistance, they generate carbon monoxide or carbon dioxide when used in an oxidized atmosphere such as in the ambient air and are gradually worn away. For this reason, there exists a drawback in that a sufficient life duration cannot be obtained.
In semiconductor manufacturing processes such as large scale integration (LSI) of recent years, a process for oxidizing a silicon surface, a process for diffusing a dopant element such as phosphorus or boron in silicon, and the like each require heating processing at temperatures of 1,000.degree. C. or higher, and also require the heating of a silicon wafer directly from a lower portion thereof to form various functional films. When a heater member formed of a metallic material or containing a significant amount of a heavy metal is used in such a process, there is a possibility that a wafer be contaminated during the process. Further, gases having special corrosiveness must be used during the various processings or during post-treatment furnace washing. Accordingly, in consideration of the ease of reaction with such gases, it cannot be said that a heater member formed of a metallic material or a heater member formed of a carbon material can be suitably used.
In view of the above-described circumstances, there has been the need for a heater member which is stable in any of various atmospheres, such as an oxidizing atmosphere and a corrosive-gas atmosphere, and which does not cause any contamination due to the metallic elements contained therein. In recent years, a ceramic heater member is used to satisfy this purpose, and particularly, silicon carbide which has a high heat resistance has come to be noticed. Silicone carbide currently used is porous silicone carbide which causes relatively less contamination by metal and which can be obtained without the addition of a metal-based sintering auxiliary. However, this material has drawbacks in that abnormal heat generation is caused by localized non-uniformity of the resistance distribution and deterioration in performance over time is caused by a reduction in the mechanical strength.
In order to overcome the above-described drawbacks, a silicon carbide rich film is formed by chemical vapor deposition (CVD) or physical vapor deposition (PVD) on the surface of a conventional heater member formed of a carbon material or the like, to improve resistance to a corrosive atmosphere and the like. However, in this case, the silicon carbide film is a thin film and thus separates from a base material due to the difference between the coefficients of thermal expansion of the base material and the coating film, thereby resulting in deterioration of durability.
Accordingly, a silicon carbide sintering process and a sintered body with no harmful additives, which are suitable for the above-described fields of application, are desired. For example, there have been proposed the following methods in which a gas or a solution, containing silicon and carbon, is used as a raw material: (1) a method for producing a sintered body in such a manner that very fine powder is formed by vapor phase epitaxy and is used as a material for the sintered body; and (2) a method for producing a plate-shaped molded body (sintered body) directly by vapor phase epitaxy.
However, these methods each have disadvantages in that productivity is low and cost is high. Further, the above method (1) also has disadvantages in that the resultant powder is too fine and particles are apt to be generated even after sintering, and method (2) has disadvantages in that it is difficult to obtain a thick molded body and it is not easy for the obtained molded body to have a volume resistivity of 10 .OMEGA.cm or less which is suitable for a heater member.